Particles are trapped and steered by feedback control. 1) The actual position of the
particles is sensed and compared to the desired positions. 2) A correcting flow and/or
electric field is computed, and then actuated, this field moves all the particles from
where they are to closer to where they should be. 3) The process repeats at each time to
achieve particle trapping or steering.

Figure 1:Feedback control particle steering approach for a single particle. A micro-fluidic device with
standard electroosmotic actuation is observed by a vision system that informs the control algorithm of
the current particle position. The control algorithm compares the actual position against the desired
position and finds the actuator voltages that will create a fluid flow, at the particle location, to
steer the particles from where it is to where it should be. The process repeats continuously to steer
the particle along its desired path. (Figure and caption taken from
[Armani06].

Both our work (Shapiro et al. [Shapiro2002],
[Armani04], [ArmaniFeb05], [Armani Mar05], [ArmaniNov05], [Chaudhary06], [Armani06]) and the ‘ABEL
trap’ work of Cohen and Moerner at Stanford ([Cohen04],
[CohenFeb05], [CohenMar05],
[CohenMar05a],
[CohenMar05b], [CohenAug05],
[CohenAug06]), uses feedback control to trap and steer one or multiple particles (us)
or just one particle (Cohen, Moerner).

We did this first (in 2002 [Shapiro2002]). Subsequently,
and to our best knowledge independently, Cohen and Moerner came up with their concept in
2004 (two years later [Cohen04]).

Click on the boxes in the timeline below to view available documents.

Figure 2: Timeline.
Relevant dates are shown: submission dates for patents and publications (presentation)
dates for journal papers (conferences). (Unpublished disclosures are shown in the
dashed line boxes.) We did not submit a journal paper until we had
demonstrated control of multiple particles at once, which includes an ability to control
one particle individually.

We are focused on manipulation of objects (e.g. cells) in cheap micro-fluidic (PDMS or
glass) devices, we can steer multiple particles at once to 1
mm accuracy (this accuracy is set by the optical
resolution of our microscope). We have developed sophisticated and robust control algorithms
to achieve our goals. Cohen and Moerner are focused on single molecule spectroscopy, they can
trap and steer only one particle using a simple control scheme. But they can do so with
higher accuracy (80 nm) based on their better optical resolution, which they achieve by
using a more expensive microscope or by sensing the output of a rotating laser beam (this laser sensing
scheme is new/novel compared to our work -- it was first proposed by Joerg
Enderlein, then first implemented by Enrico Gratton, and taken to the
shot-noise limit and expanded to single quantum dot tracking in 3D by
Berglund, McHale, and Mabuchi http://minty.caltech.edu/Tracking/.

If you believe that any statements on this
page are factually incorrect, please send me an email to
benshap@eng.umd.edu along with a brief explanation
plus attached documentation. If there are any factual errors, I will correct
them.

References

In chronological order: from first to last. Blue for our
work, green for Cohen/Moerner.